The present invention relates to a vehicle control system for controlling a ratio (a driving force distribution) between a driving force transmitted to rear wheels and a driving force transmitted to front wheels, and further controlling a front or rear wheel steer angle.
The above-mentioned application (19) proposes a driving force distribution control system arranged to increase a driving force to a front or rear wheel pair whose speed is lower than the speed of the other pair with an increase of the front and rear wheel speed difference. When this control system is applied to a vehicle in which the rear wheels are always driven, this control system increases a front wheel driving force transmitted to the front wheels with an increase of the front and rear wheel speed difference due to slippage of the driven rear wheels. When the slip of the rear wheels is reduced by increasing the front driving force, then this control system decreases the front wheel drive force. In this way, this control system maintains an optimum driving force distribution between the front and rear wheels.
When the vehicle is accelerated during a turn, the slippage of the rear wheels increases the oversteering tendency. In this case, this driving force distribution control system increases the understeering tendency and restore the steering characteristic of the vehicle to the neutral steer by increasing the front wheel driving torque with an increase of the front and rear wheel speed difference. When, on the other hand, the understeer is increased by slippage of the front wheels, this control system increases the oversteer to restore the steering characteristic to the neutral steer by increasing the driving force transmitted to the rear wheels. However, in a transient period from a change in the steering wheel angle until the steering characteristic is restored to the neutral steer, there appears an initial understeer or an initial oversteer corresponding to the front and rear wheel speed difference.